The polymers based on aliphatic diols derived from biologically based resources are of great interest in the plastics industry and for the manufacturing industry for the preparation of materials and products that can be derived from inexpensive, renewable sources and that are also biodegradable and thereby have a low net environmental impact. The polymer that are of particular interest are based on isosorbide and more specifically referred to as 1,4:3,6-dianhydro-D-sorbitol, referred to hereinafter as isosorbide, the structure of which is illustrated below, is a chiral and relatively thermostable diol that is readily made from sugars and starches.

It is opined that secondary alcohols such as isosorbide have poor reactivity and are sensitive to acid catalyzed reactions. As a result of the poor reactivity, polymers made with an isosorbide and acid monomer are expected to have a relatively low molecular weight.
References may be made to Journal, Biomacromolecules 2010, 11, 1196-1201″ wherein copolyesters of L-lactic acid and isosorbide is reported. Similarly, the copolymers of lactic acid with succinic anhydride, butane tetra carboxylic acid or cyclohexane carboxylic acid were also prepared by step growth polymerization. However, the copolymers obtained had very low molecular weights and glass transition temperature.
References may be made to patent US20080108759, wherein improved polylactic acid polymers comprising units derived from lactic acid, isosorbide and poly carboxylic acid has been disclosed. It is further stated by the inventors that they have now discovered that the incorporation into a lactic acid polymer of units derived from isosorbide and units derived from a poly carboxylic acid can give a polymer having the desired higher glass transition temperature. Although isosorbide is known to elevate the glass transition temperature in certain other polymers, it is ineffective in lactic acid polymers and the presence of a poly carboxylic acid is necessary if the desired results are to be achieved. Similar advantages may be expected by the incorporation of these units into poly lactide polymers. Moreover, by appropriate selection of the relative amounts of the components of the polymer, it is possible to ensure that the polymer has a relatively high degradation temperature, an important consideration for materials used by the public.
Main objective of the present invention is to provide lactic acid-isosorbide copolyester with improved properties such as glass transition temperature (Tg), melting temperature (Tm) and crystallinity from renewable resources.
Another objective of the present invention is to prepare high molecular weight lactic acid-isosorbide copolyester with high glass transition temperatures (Tg's) with the quantitative incorporation of isosorbide (>90%) by a combination of polymerization techniques namely, melt phase disproportionation followed by solid state polymerization, solution phase disproportionation followed by solid state polymerization.